Removal of chromium (VI) from aqueous solutions using quaternized chitosan microspheres

In this study, quaternized chitosan microspheres (QCMS) were prepared and its Cr (VI) removal potential was investigated. Batch experiments were conducted to examine kinetics, adsorption isotherm, pH effect, and thermodynamic parameters. Equilibrium was attained within 50 min and maximum removal of 97.34% was achieved under the optimum conditions at pH 5. Adsorption data for Cr (VI) uptake by the QCMS were analyzed according to Langmuir, Freundlich, and Temkin adsorption models. The maximum uptake of Cr (VI) was 39.1 mg.g(-1). Thermodynamic parameters for the adsorption system were determinated at 293 K, 303 K, 313 K and 323 K. (Delta H degrees = 16.08 kJ.mol(-1); Delta G degrees = -5.84 to -8.08 kJ.mol(-1) and Delta S degrees = 74.81 J.K-1.mol(-1)). So the positive values of both Delta H degrees and Delta S degrees suggest an endothermic reaction and increase in randomness at the solid-liquid interface during the adsorption. Delta G degrees values obtainedwere negative indicating a spontaneous adsorption process. The kinetic processwas described by a pseudo-second-order rate equation very well. The results of the present study indicated that the QCMS could be considered as a potential adsorbent for Cr (VI) in aqueous solutions. (C) 2016 The Chemical Industry and Engineering Society of China, and Chemical Industry Press. All rights reserved.